159430 - Effect of spray characteristics on the evaporation and decomposition of a urea-water-solution Master of Science Thesis JORUN WEDLUND Department

159430 - Effect of spray characteristics on the evaporation...

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Effect of spray characteristics on the evaporation and decomposition of a urea-water-solution Master of Science Thesis JORUN WEDLUND Department of Chemical and Biological Engineering Division of Chemical Reaction Engineering CHALMERS UNIVERSITY OF TECHNOLOGY Gothenburg, Sweden, 2012
Influence of spray characteristics on the evaporation and decomposition of a urea-water-solution JORUN WEDLUND © JORUN WEDLUND, 2012. Department of Chemical and Biological Engineering Chalmers University of Technology SE-412 96 Göteborg Sweden Telephone + 46 (0)31-772 1000
iii Influence of spray characteristics on the evaporation and decomposition of a urea-water-solution JORUN WEDLUND Department of Chemical and Biological Engineering Chalmers University of Technology Abstract Even though urea-SCR is a well-established technique to reduce emissions of nitrogen oxides from diesel engines it is not without problems. The residence time in the silencer is limited and it is therefore necessary to have a well designed system where the urea solution can evaporate quickly. Moreover, deposit formation may occur if the system is not properly designed. The characteristics of the spray has been identified as one the parameters that may affect the evaporation of urea as well as the formation of deposits. In this thesis the influence of certain spray characteristics on the evaporation of AdBlue as well as wall film formation has been investigated. An experimental investigation has been done in a test rig that was designed to obtain a plug flow. Investigated spray characteristics includes the dosing unit pressure, the spray angle and the dosing frequency that could all influence the droplet size of the spray. The evaporation rate has been estimated from FTIR measurements as well as temperature measurements on a wheel inserted in the pipe. The estimated depletion times based on earlier experimental data indicate that the difference for the investigated droplet sizes should be large. The FTIR measurements did not indicate significant effects for any of the tested parameters. For high temperatures the differences are small and could be due to differences in the radial distribution. For low temperatures liquid AdBlue still remains that disturbs the FTIR signal and could be converted to ammonia in the filter of the FTIR instrument. The evaporation rate was better captured with the temperature measurements where significant effects could be observed for lower temperatures and flow rates. Also it was possible to capture the radial distribution of the spray. It was however observed that a plug flow was not obtained and that droplets were entrained towards the upper part of the pipe. The temperature measurements indicate that the larger droplets that are produced with a lower dosing unit pressure leads to a significant decrease in the evaporation rate for low temperatures and gas flow rates. The droplets are also distributed over a smaller area which leads to more entrainment and therefore also more wall wetting for these flow conditions. A

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